The invention relates generally to a method of sealing a metal halide battery. More particularly, the invention relates to a method of sealing a ceramic separator to a metal component in the metal halide battery. The invention also relates to a sealing structure for a metal halide battery, formed by using such a method.
Development work has been undertaken on high temperature rechargeable batteries/cells, using sodium for the negative electrodes. The liquid sodium anode is separated from a cathode by a sodium-ion conducting solid electrolyte separator. The anode and the cathode are sealed from each other at atmospheric pressure. Suitable materials for the solid electrolyte separator include beta alumina and beta″ alumina, known as beta alumina separator electrolyte (BASE). Usually, these batteries or cells have a metallic casing, and may also have other metallic components.
Ceramic components of the cell are typically joined via a seal glass. Metallic components are often joined by welding or thermal compression bonding. However, ceramic-to-metal bonding in the high temperature cell may crack, due to thermal stress caused by a mismatch in the coefficient of thermal expansion for each material. Thus, the bond may have a limited life, and bond failure may cause cell failure.
A common bonding technique uses a porous metal layer applied in the form of paste or ink, which then combines with a glassy phase from the ceramic separator, by wicking or capillary action. The metal layer is often screen-printed. This metal layer is then bonded to the metal component by diffusion bonding or brazing. However, this process requires close process control to assure strong, hermetic, defect-free bonds, and the complexity of such control may make the process economically unsuitable.
Furthermore, the battery application prefers the use of a high purity alumina to address corrosion concerns. However, the above process is not amenable to high-purity alumina, because little or no glass phase is available to promote bonding.
It would therefore be desirable to develop new methods for efficiently sealing metal halide batteries.